Airbags for motor vehicles are known and have been used for a substantial period of time. A typical construction material for airbags has been a polyester or nylon fabric, coated with an elastomer such as neoprene, or silicone. The fabric used in such bags is typically a woven fabric formed from synthetic yam by weaving practices which are well known in the art.
The coated material has found acceptance because it acts as an impermeable barrier to the inflation medium. This inflation medium is generally a nitrogen gas generated from a gas generator or inflator. Such gas is conveyed into the cushion at a relatively warm temperature. The coating obstructs the permeation of the fabric by such hot gas, thereby permitting the cushion to rapidly inflate without undue decompression during a collision event.
Airbags may also be formed from uncoated fabric which has been woven in a manner that creates a product possessing low permeability or from fabric that has undergone treatment such as calendaring to reduce permeability. Fabrics which reduce air permeability by calendaring or other mechanical treatments after weaving are disclosed in U.S. Pat. No. 4,921,735; U.S. Pat. No. 4,977,016; and U.S. Pat. No. 5,073,418 (all incorporated herein by reference).
The coating of a fabric with an elastomer such as neoprene typically requires the application of that elastomer from a solution in a volatile solvent. This solvent must then be evaporated and the elastomeric system cured. Typical dry coating weights for neoprene have been in the range of about 1 ounce per square yard or greater. Silicone coatings typically utilize either solvent based or complex two component point of application reaction systems. Dry coating weights for silicone have been in the range of about 0.7 ounces per square yard or greater. As will be appreciated, high add on weights substantially increase the cost of the base fabric for the airbag as well as making the eventual sewing of the fabric into an airbag structure more difficult.
The use of certain polyurethanes as coatings as disclosed in U.S. Pat. No. 5,110,666 to Menzel et al. (incorporated by reference) permits low add on weights reported to be in the range of 0.1 to 1 ounces per square yard but the material itself is relatively expensive and is believed to require relatively complex compounding and application procedures due to the nature of the coating materials. Patentee, however, utilizes strictly linear thermoplastic polyurethanes within his coating and permits above 0.5 ounces per square yard of such a coating to be present on the fabric. Such teachings clearly do not anticipate or fairly suggest the required coatings and amounts present of such coating on the inventive airbag fabric.
In light of the background above, it can be readily seen that there exists a need for an airbag base fabric which provides controlled low permeability through use of a coating which provides an effective barrier to air permeability while nonetheless avoiding the inherent complexity and cost of materials which have heretofore been utilized. Accordingly, this invention is directed to a coated base fabric for an airbag comprising a polyester or polyamide substrate fabric coated with a porosity blocking layer of a cross-linked elastomeric coating resin. The term porosity blocking layer is intended to encompass the amount necessary to obtain a fabric which possesses suitable air permeability characteristics while also providing a coating which passes a storage separation (or blocking) test. Any stable elastomer resin can be utilized within this invention as long as the resin is cross-linked on the fabric surface and is applied at a coating weight of between about 0.1 and 0.5 ounces per square yard of fabric. By stable elastomer resin, it is meant that such a resin exhibits a glass transition temperature (T.sub.g) of below room temperature (i.e., from about 20 to about 25.degree. C.). Such a T.sub.g measurement indicates the presence of elastomeric properties for the specific material. Of particular interest as cross-linked stable elastomeric resins are polyamides, polyurethanes, and hydrogenated NBR, EPDM, butyl rubber, and acrylic rubbers.
When a thin coating of cross-linked elastomeric resin is added to airbag fabric, it has discovered that such a fabric exhibits superior blocking test results as well as necessary and beneficial air permeability characteristics, particularly in view of the prior art. Other objects and advantages of the invention will become apparent upon reading the following detailed description.
The cross-linking requirement is of utmost importance in this invention since it was discovered that the beneficial properties were obtained solely through the utilization of a cross-linked elastomeric resin. Such a cross-linked coating is produced through the addition of a cross-linking agent to the coating formulation or is supplied through the utilization of a self-cross-linking resin. Cross-linked resins provide the necessary mechanical properties (i.e., enhanced tensile strength) and aging stability for the elastomeric resin coating at the requisite low coating weight level. A non-cross-linked resin does not provide such necessary properties.
While the invention will be described and disclosed in connection with certain preferred embodiments and practices, it is in no way intended to limit the invention to those specific embodiments, rather it is intended to cover equivalent structures structural equivalents and all alternative embodiments and modifications as may be defined by the scope of the appended claims and equivalence thereto.